If you want to be a little more informal, you could ask "Where's my stuff?"

Where are my things? Have you seen my things? Has anyone seen my things? Where did I put/leave my things? I wonder where my things are. ...

Your way of asking is perfect! Depending on what your "things" are, you may get more specific. If you know that someone else has moved your things, you could ask "where did you put my things/stuff?"

This is not at all a common way, but my mother would say something like "What happened to my keys? They have jumped off of the planet."😀

You could definitely say, "Where are my things?" That is perfectly correct, but I think it is more common to say, "Where's my stuff?"